Modulated carrier wave receiver



Feb. 1, 1944. 1 A M|' E L I 2,340,730

' MQDULAI'ED CA-RRIER WAVE RECEIVER Filed July 2, 1937 2 Sheets-Sheet 2 NEGATIV' FEED E/ICK NE 54 5 7 A/t'TWORk INVENTORS ALA/V 0- BLUMLE/N WILL/AM ll- (IONA/ELL ATTORNEY Patented Feb. 1, 1944 MODUIATED CARRIER WAVE RECEIVER Alan Dower Blumlein, Ealing, London, and William Horace Connell, Hillingdon, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application July 2, 1937, Serial No. 151,618

v In Great Britain July 8,1936

12 Claims.

This invention relates to modulated carrier wave receivers. The invention has particular, but not, exclusive application to modulated carrier wave receivers of the superheterodyne type.

Various attempts have been made with a View to providing means for varying the selectivity of receivers, either manually, or automatically with the strength of the received signals, and in cases where selectivity is controlled automatically, it has been proposed to employ a valve shunted across the circuit the selectivity of which is to be controlled, the valve being fed with rectified currents, corresponding to the received signal strength for varying its shunting effect whereby the response curve of the circuit is likewise varied. Such an arrangement is, however, expensive owing to the provision of the additional valve shunting the circuit.

It is the chief object of the present invention to provide an improved circuit whereby variations of the selectivity can be obtained either manually or automatically as the signal strength varies, or by a combination of automatic and manual means.

It is also an object of the invention to provide a receiver which will give a balanced reproduction of sound signals even when the selectivity is varied.

According to one featur of the invention, a modulated carrier wave receiver is provided comprising a thermionic valve provided with means for effectively producing a wholly or partially negative feed back of voltage to a control electrode of the valve, the magnitude of the feedback varying with frequency for the purpose of modifying the frequency response of the receiver and means for changing th operating characteristics of said valve whereby the effect of the voltage feedback is modified. Preferably, the effect of the feedback on the frequency response of the receiver is modified by varying the slope of the valve by variation of the bias potential, and where automatic selectivity is required this may be efiected by applying to one of the control electrodes of said valve volume or gain control bias potentials, derived in known manner.

If desired the said valve may be included in a stage of amplification associated with another stage of amplification including another thermionic valve so linked with the first mentioned valve, that the change in the gain of each amplifier stage under the action of the volume or gain control bias potential is difi'erent in each stage, whereby the eifect of the negative feed back can be controlled independently of the amount of applied automatic volumecontrol bias, and means may be provided whereby the distribution of volume control bias potentials to each of the two linked stages may be adjusted manually.

An arrangement according to the invention may also be used to adjust the balance of reproduced sound, in a receiver where the selectivity is changed as the strength of the received signals changes. In this case the feedback according to the invention may operate on the low or bass frequencies of the reproduced'sound in a manner corresponding to the way in which th high frequencies thereof are affected by the variation of the selectivity.

The feedbackof voltage according to the invention may be obtained from an impedance which is common to the anode-cathode path and to the control grid-cathode path of the valve, said impedance being arranged to be of low value for one frequency in the signal band and of higher values 'forthe frequencies in the signal band remote from that frequency. In a carrier wave receiver of-the superheterodyne type in which the invention is applied for producing automatic variation of selectivity with varying signal strength, the invention will usually be applied to a stage of intermediate frequency amplification and the aforesaid impedance will usually be made of low value'for the intermediate frequency of the receiver. In a superheterodyne receiver a selectivity control. according to the invention may be applied to the frequency changer valve of the receiver, In other carrier wave receivers the invention will usually be applied in connection with a stage of carrier frequency amplification. I

In order that the said invention may be clearly understood and readily carriedinto effect, the same will now be described-with reference to the accompanying drawings in which:

Figs. 1 and 2 illustrate circuits embodying th basic principles of the invention,

Figs. 3A, 3B, 3C and 3D illustrate modifications of the cathode circuits ofthe arrangements shown in Figs. 1 and 2 and Figs. 4 to 9 illustrate further embodiments of the invention. In the drawings similar components are indicated by the same reference numerals.

Referring now more particularly to Fig. 1 of the accompanying drawings, the reference numerals I and 2 represent respectively the input and output circuits of an intermediate frequency amplifying valve 6, shown as a screened grid valve of the variable mu type, the invention. as

will be appreciated, being described for use in a superheterodyne receiver. The invention is also described in this figure in conjunction with automatic volume or gain control the purpose of which will be hereinafter more fully explained.

The input circuit I is coupled to the control grid of the valve 6 and is decoupled to earth by a condenser 3, automatic volume or gain control potential derived in any suitable manner being applied to the control grid of valve 6 through resistance 4 from a line 5 denoted'by the letters A. V. C. Negative feed back for the valve .6 is .obtained by the provision of an inductance Ia and series condenser Ib in the cathode lead of the valve 6, the feed back circuit being generally designated by the dotted line rectangle I. For the purpose of by-passing anode currenta choke 8 is provided in parallel with the circuit I, the choke 8 being roughly tuned if desired with the parallel condenser shown. The circuit I is arranged to present a low impedance at its resonant frequency as by tuning the circuit to the same frequency as the circuits I and 2 which, in the case of a superheterodyne receiver, corresponds to the intermediate frequency of the receiver. At this frequency a small negative feed back is provided by the residual resistance of the circuit I, and for side-band frequencies the impedance of the circuit I increases, thus reducing the gain for such side-band frequencies. If the slope or mutual conductance of the valve is high, the feed back will attenuate or cut off the sidebands, but at low slopes the effect of the feed back will be negligible. In the example of Fig. 1 the slope of the valve measured in terms of cathode current will be the combined "slope to screen and anode, but in the example shown in Fig. 2 which illustrates a'modification of that shown in Fig. 1, and in which like reference numerals indior the effective ratio of the slopes with and without negative feed back will be As stated above, 2 is small at carrier frequencies and larger at side-band frequencies, so that, providing z is sufficiently great, there will be an attenuation or cut-off of side-band frequencies and a corresponding increase of selectivity. This increase in selectivity Will be most noticeable when g is large, that is to say, when there is little automatic volume control negative bias as when distant stations are being received. On a local station the automatic volume control voltage will increase the bias thus reducing the slope of the valve and 50 making the negative feedback, and hence the extra selectivity, negligible. Thus it will be appreciated that with the circuits shown in Figs. 1 and 2, automatic variable selectivity occurs, the selectivity decreasing when local stations are being received and. increasing with more distant stations. It will be understood that instead of employing the automatic volume control to vary the slope of the valves 6 for selectivity control, the bias on the valves may be adjusted manually, or alternatively, a manual control may be employed in addition to the automatic volume control potentials so that the slope of the valves may be maintained high thereby extra selectivity is available for a less distant station which is subjected to unusually severe interference.

The circuit I of Figs. 1 and 2 may be replaced by'the corcuits shown in Figs. 3A, 3B, 3C and 3D. In Fig, 3A an inductance I0 is bridged across the condenser .Ib so as to by-pass the anode current thus obviating the use of the inductances 8 of Figs. 1 and 2. The inductance is may be made sufdciently high to avoid a parallel resonance with the associated condenser Ib within the working range, the circuit shown in Fig. 3A being tuned by the condenser Ib so as to present a low impedance at the carrier or intermediate irequency for the reasons referred to above.

In Fig. 3B the circuit I is replaced by a condenser Id shunted by an inductance la in series with another condenser If shunted by an inductance Ig. The circuit of Fig. 3B can be adjusted to present a low impedance at the carrier frequency and a high impedance at two frequencies on either side of the carrier frequency so that a comparatively sharp out can be effected at the undesired side-band frequencies Without necessitating the high coil efficiency required in the circuits of Figs. 1, 2 and 3A.

Fig, 3C illustrates a modification of the circuit of Fig. 3B, in which an inductance coil In in series with a condenser 1i is shunted by a condenser 1] and by a parallel inductance Is. The circuit of Fig. 3C is less difficult to adjust than the circuit of Fig. 33. For adjusting the circuit of Fig. 30, the inductance In and condenser I1 are'disconnected and the condenser I; and inductance 'I-k are tuned to the carrier frequency to afford maximum negative feedback, that is a reduction of gain at the carrier frequency. The

inductance In and condenser I1 are then connected and tuned to pass the carrier frequency, the circuit then affording an approximately symmetrical cut-off of side-bands on each side of the carrier frequency.

The circuit shown in Fig. 3D is similar to that shown in Fig. 3G with the diiference that the coil In is shunted by a condenser I1 which permits the use of a smaller inductance for the cell 111. Typical values for the components of the circuit 3D arefor a carrier frequency of Inductance In microhenries 3125 Condensers hand I1 micro-microfarads 250 Inductance 1k microhenries 31.25 Condenser 11 micro-microfarads 50000 inductance/capacity ratio.

valve having a slope of 4 milliamps per volt, will therefore lose 1.6 decibels gain at the carrier frequency and 20.8 decibels gain at a frequency 3200 cycles per second off the carrier frequency. A reduction of slope to 0.4 milliamps per volt will make the carrier loss negligible and at a frequency of 3,200 cycles per second'ofi' the carrier frequency the loss will be about 6 decibels. At 0.04 milliamps per volt, both losses will be negligible.

With the circuits shown, especially with that of Fig. 1, there may be a tendency for oscillation. since with a capacitive cathode load the input impedance of the grid (due to grid-cathode capacity) has a negative resistance component. In the construction shown in Fig. 4 (in which only the grid and cathode circuits are illustrated) a neutrodyning condenser II is provided to prevent such oscillation. The choke 8, which corresponds to the choke 8 of Fig. 1, is extended by a further portion giving a potential opposite to that of the cathode. The condenser II approximates to the grid-cathode capacity, assuming equal efiective ratio for the two portions of the choke 8. Similarly, the inductance Is of Fig. 3D may be extended downwards and condenser I correspondingly decreased so as to provide a neutrodyne potential. In practice, the inductance 11; may with advantage consist of a small part of a much larger coil, the condenser I1 being then bridged across the whole coil, thus requiring a much smaller value for condenser I1; the neutrodyne voltage can then be obtained from a further tapping point along this coil.

Fig. shows a further alternative which enables a less eflicient circuit I to be used than that required by the arrangement of Fig. 1. The resistance of circuit I in Fig. 1 at resonance causes feed back at the carrier frequency, thus reducing the gain and reducing the difi'erence of feedback for carrier and remote side-band frequencies. In Fig. 5 a tightly coupled and roughly tuned choke is provided having tappings I3, I4, I5 and I6 connected as shown. If the ratio between I3, I4 and I4, I5 is unity, and if resistance I2 equals the tuned resistance of circuit I, no feed back will be produced at resonance, assuming negligible leakage inductance between I 3, l4 and I4, I5, since the bridge will be balanced. At the side-band frequencies, however, negative feed back will be produced. The grid circuit decoupling condenser 3 may be connected at I5, but is preferably taken to a more remote tapping point I6 as shown. In efiect, a step-up of feed back is obtained between the tapping points I4, I5 and I4, I6. This arrangement does not require such a high impedance for circuit I, which might otherwise require an inconveniently high To prevent oscillation, the neutrodyne condenser II may be provided connected to an extension II of the roughly tuned coil. If desired, the resistance I2 may be replaced by a parallel resonant circuit affording a resistance equal to resistance I2 at its resonant frequency and so serving to earth the tapping point I5 at frequencies remote from the carrier frequency. Many other alterations of this bridge circuit are possible. For example, the circuit I may even be replaced by a comparatively high resistance and the resistance I2 replaced by a parallel tuned circuit, thus obtaining a similar effect to that which results when the resistance I2 is replaced by a parallel resonant circuit as aforesaid. Similarly, the bridge circuit may be placed in the anode decoupling lead as in Fig. 2.

This would correspond to earthing the cathode and tapping I4, and returning the anode decoupling condenser to the junction of the circuit I and resistance I2. With the screen of the valve 6 earthed, tapping I1 and the neutrodyne condenser would not be required. If the decoupling condenser (not shown) usually associated with the screen of valve 6 were also returned to the junction of circuit I and resistance I2 (to increase the effective slope), then the tapping point I! would require to lie on the other end of the choke, (beyond the point I3) and condenser II would neutrodyne the screen to grid capacity of the valve.

With the bridge circuits shown, small positive feed back may be introduced at the carrier frequency, as for example, by making the resistance I2 slightly greater than the resistance of the circuit I at its resonance. This, however, will not alter the operation, since for frequencies remote from carrier frequency the required selectivity will be obtained by introducing negative feed back, as against the positive feed back for the carrier frequency.

The invention may also be applied to receivers other than of the superheterodyne type, in which case the circuit I would be arranged to be tunable with the other circuits. Similarly the invention may be applied to more than one amplifier stage.

Fig. 6 shows the invention as applied to the mixing valve (a hexode valve being shown) of a superheterodyne circuit, the bias on the signal grid (the third grid from the cathode) of the mixing valve being varied by the application thereof of bias potentials derived from an automatic volume control circuit. In this figure the tuned input circuit is indicated by the reference numeral I, automatic volume control potentials being applied through the resistance 4 from the line 5, the signal grid being decoupled to earth by condenser 3. The intermediate frequency anode circuit is indicated at 2. Th screening grids are fed through a high impedance choke Ba decoupling condenser being provided between the screening grids and cathode as shown. Local oscillations are fed between the cathode and the first grid of the mixing valve, the source of local oscillations being conventionally represented in the figure. The intermediate frequency anode currents fiow through circuit I and cause negative feed back of intermediate frequency voltage between the signal grid and cathode. The circuit 1 is of the type shown in Fig. 30 so as to by-pass the radio frequency currents through the shunt condenser shown.

If desired, a switch may be arranged to remove the automatic volume control bias from a valve having selective feed back, to enable the selectivity to remain for large input voltages if required. However, the removal of the automatic volume control negative bias may cause too much output from the receiver, unless there is an efficient automatic volume control, operative also on earlier valves. The same switch may, therefore, be arranged to make the bias of the earlier valves more negative and so counteract this effect.

Fig. 7 shows a modification of the invention. In this figure the valve 6 having the negative feed back circuit I in its cathode lead is associated with a further amplifier valve I6. Automatic volume control bias potentials are applied to the grids of the two valves, the bias potential of the automatic volume control line in this case is arranged to be at a positive potential to earth for :maximum gain. The cathodes of the two valves l6 and 6 are given a positive potential by means of resistances 22 and 2| in their cathode leads. The resistance 22, however, is smaller than the resistance ill, but is connected to the high tension supply through a resistance 23 which supplies extra steady current to maintain the cathode of valve I6 positive. An increase of signal strength causes the automatic volume control line to become less positive or more negative, causing a drop in anode currents. A drop of the current in-valve B effectively lessens the positive potential on its cathode and so counteracts the change of bias. A similar effect takes place in valve IE, but as resistance 22 is less than resistance 2 l the effect is less marked, and so valve 15 is biased more negatively than valve 6. This prevents the selectivity decreasing too rapidly with increase of signal strength. An interchange of resistances 22 and 23- with resistance 2i would produce the reverse effect. Valve I may of course be a high frequency mixing valve or an intermediate frequency valve.

Fig. 8 of the drawings shows a combined automatic and manual selectivity control. The arrangements of the two valves 6 and I6 is similar to that shown in Fig. 7, the biasing resistances 2| and 22 in this case, however, being equal. The resistance 23 feeds current from the high tension supply to cathodes of the two valves shown through the potentiometer 24. By adjusting the point of connection of the resistance 23 and potentiometer 24 to the left, the positive cathode potentialis increased on the first valve and decreased on the second so increasing the feed of the second valve and thus increasing the selectivity while keeping the gain approximately constant. It is also found with variable selectivity that it is advantageous to cut the very low modulation frequencies at the same time as cutting the very high modulation frequencies, in order to preserve a better balance of the sound output. The invention can be applied to perform this bias cut automatically at the same time as the higher modulation frequencies are cut. Fig. 9 shows such a circuit in which automatic volume control is also employed in conjunction with one of the low frequency amplifying stages to maintain the sound output substantially constant. This feature may be applied generally to low frequency amplifiers in order to provide tone adjusting means. In this circuit, 23 represents the last intermediate frequency valve of a superheterodyne circuit, and Zi and 22 are coupled circuits arranged as shown, the circuit 2| being connected to a source of anode current not shown. The anode 29a of a double diode valve 2 3 supplies automatic volume control voltage to the automatic volume control line 5, which voltage is developed across resistances 25. 26, 21 and 28 connected as shown. 'The automatic volume control bias potentials are applied by line 5 to one or more of the preceding stages, in which the circuit 1, for affording a negative feedback which varies with frequency, is associated with one or more of said stages as described above. The resistance 2'! is comparatively small and is used with condenser 34 to decouple any possible modulation frequency arriving from resistances 21 and 28 arranged between the cathode and earth of a low frequency amplifier valve 35 shown as a pentode. A delay for the'automatic volume control is provided both by the voltage drop across-the resistance 21 and also by the potentiometer 29,30c0nnected to the high tension supply,-the cathode of valve- 24 being *decoupled to earth by condenser 38. This latter potentiometer draws comparatively little current incomparison with the current of the low frequency'amplifier valve 35. This valve obtains its bias through potentiometer 33, and resistance 3| from a tapping on the resistances 25, 23 and 21 across which the automatic volume control potentials are developed. The grid bias is decoupled to earth by a condenser 31. The word delay is not intended to imply any time delay but has the significance attributed to the word when employed in the term delayed automatic volume contro Suppose that a delay of 7 volts is provided on the cathode of valve 24 and suppose also that approximately 21 volts bias, not allowing for the change in potential of the cathode of valve 35, is required to reduce the preceding valves to their minimum sensitivity then there will be a. change of signal strength over the Whole automatic volume control range of 4:1. The tapping providing the grid bias of valve 35 is so chosen as to change the slope of this valve by about 4:1 in this range, so that the final output for the same modulation depthis maintained approximately constant. This involves a rather large current in valve 35, which may necessitate a transformer coupling to the output valve in place of the resistance capacity coupling-shown, if overloading is to be prevented at the position of minimum slopeu A rectified modulation input for valve 35 is obtained from the anode 29 of diode 23 across the load circuit 32 and potentiometer 33. Further smoothing may be introduced at this point if required in order to remove any intermediate frequency input to the valve 35. The cathode load of valve 35 is composed of resistances 21 23 shunted by condenser 36. This combined resistance is preferably made several times the inverse of the mutual conductance or slope of the valve. If condenser 36 is not made sufliciently large, a loss of low frequencies will occur when the inverse of the mutual conductance of valve 35, in parallel with the cathode resistance is less than the impedance of the condenser at the low frequencies. This bass loss, will be much less marked when valve 35 has a low slope, since the impedance of condenser 35 will no longer be high compared with the slope. Thus an automatic cut-off of the bass frequencies will be obtained for distant stations in the same manner as the automatic cut-ofif of the high frequencies prior to the detector. If preferred, high frequency cut-off may also occur after the detector, as for example, by inserting an inductance in series with condenser 36, so as to introduce the negative feed .back again for the higher modulation frequencies. This may be employed independently or in conjunction with the attenuation of the bass response. As the valve 35 does not change its slope (in the example given) as much as do the earlier variable mu valves, this high frequency cut-off cannot be made as sharp nor will it be found as satisfactory as the high frequency cutoff applied in the manner described in the preceding examples. Valve 35 may be one of the variable mu type or may be a valve with a substantially straight characteristic curve having a remote anode current cut-off.

The circuit shown in Fig. 9 is intended to operate so as toprovide a potentia1 on the automatic or gain control lead 5, which for weal: signals, is positive with respect to earth. The control valves must have cathode resistances which cause the cathodes at high feed to be yet more positive than this potential, so that the valves are not operating with the grids positive with reference to the cathodes. These cathode resistances may be shunted by condensers. so as to remove any negative feed-back, or may be left unshunted so as to reduce overload effect in the valve by providing negative feed-back, or finally, the resistances may be constituted by a resistance of the circuit I used to provide automatic variable selectivity, the resistance being any resistance such as the choke 8 in Fig. 1, coils 1K in Figs. 30, 3D, or the resistance l2 in Fig. 6.

In designing the circuit shown in Fig. 9, the value of combined resistance 21a and 28 is made sufliciently high to produce at maximum sensitivity the required drop in low frequency response for valve 35. Part of this resistance 28 is used to produce the standing positive potential on the lead 5 via the resistance 21 (decoupled by 34 and the resistances 26 and 25). 'The whole positive potential available on the cathode of 35 is used via resistance 29 to provide positive delay volts for the diode 24a as regards its anode 29a. In most cases it may be found that there is insumcient positive potential on the cathode of the valve 35, having regard to the positive potential already applied from resistance .28 to the anode 29a, in which event it is necessary to provide additional positive potential by means of the resistance 30 connected to H. T. positive supply. An alternative arrangement is to connect the right hand end of resistance 29 to earth and either increase resistance 29 or reduce resistance 30 to obtain the desired voltage.

In some cases, particularly with the arrangement shown in Fig. 5, it is possible to operate the circuits satisfactorily with considerably positive feed back at the carrier frequency, the feed-back still being positive despite variation in-the slope of the valve. For remote side-band frequencies, however, the feed-back is negative.

In the following claims the term carrier frequency is intended to include not only the actual carrier frequency but also the carrier frequency modified to the intermediate frequency of a superheterodyne receiver or to a second intermediate frequency in a double superheterodyne receiver.

Various modifications and alterations may be made within the scope of the appended claims.

We claim: 7

1. In a modulated carrier signal transmission network, a tube provided with at least a cathode, signal grid and plate, a signal input circuit coupled to said grid and cathode for applying thereto a band of signal frequencies whose midband frequency is of a desired carrier frequency, an output circuit connected to the plate and cathode, said output circuit being tuned to said desired carrier frequency, a reactive network 'connected between the plate and cathode of the tube and being series resonant to the said carrier frequency whereby alternating voltage developed across the reactive network has a relatively low amplitude at said carrier frequency and increasingly higher amplitudes at modulation frequency components of the said band spaced from said carrier frequency, means for impressing said a1- ternating voltage upon said signal grid in degenerative phase, and means for controlling the gain of said tube thereby to regulate the magnitude of said alternating voltage.

2. In a modulated carrier signal transmission network, a tube provided with at least a-cathode, signal grid and plate, a signal input circuit coupled to said grid and cathode for applying thereto a band of signal frequencies whose midband frequency is of a desired carrier frequency, an output circuit connected to the plate and cathode, said output circuit being tuned to said desired carrier frequency, a reactive network connected between the plate and cathode of the tube and being series resonant to the said carrier frequency whereby alternating voltage developed across the reactive network has a relatively low amplitude at said carrier frequency and increasingly higher amplitudes at modulation frequency components of the said band spaced from said carrier frequency, means for impressing said alternating voltage upon said signal grid in degenerative phase, and additional means for decreasing the said tube gain for'strong signal reception thereby-to decrease the said degenerative voltage amplitude at the spaced modulation frequencies. T I a 3. In a modulated carrier signal transmission network, a tube provided with at least a cathode, signal grid and plate, a signal input circuit coupled to said grid and cathode, an output circuit connected to the plate and cathode, said output circuit being tuned to a desired carrier frequency, a reactive network connected between the plate and cathode of the tube and being series resonant to the said carrier frequency whereby alternating voltage developed across the reactive network has a relatively low amplitude at said carrier frequency and increasingly higher amplitudes at modulationfrequency components of the modulated carrier band spaced from said carrier frequency, means for impressing said alternating voltage upon said signal grid in degenerative phase, and auxiliary means, responsive to carrier amplitude variation, for controlling the gain of said tube thereby to vary the amplitude of the degenerative voltage.

4. In a side band modulated carrier energy transmission system, an amplifier tube having at least a cathode, a signal grid and an anode, a carrier energy input circuit connected between the grid and a point of relatively fixed potential, a carrier output circuit connected to the anode, a reactive network connected between the cathode and said point, said network having an impedance which is zero at the carrier frequency and which progressively increases in value for the successive frequencies of the modulationside bands, and means for decreasing the gain of said tube automatically in response to an increase of carrier amplitude.

5. In a side band modulated carrier energy transmissionsystem, an amplifier tube having at least a cathode, a signal grid and an anode, a carrier energy input circuit connected between the grid and a point of relatively fixed potential, a carrier output circuit connected to the anode, a reactive network connected between the cathode and said point, said network having an impedance which is zero at the carrier frequency and whichfor controlling the frequency response of said amplifying means.

6. In a modulated carrier signal transmission network, a tube providedwith-at least acathode, signal grid and plate, a, signal input circuit coupled to. said grid and cathode, an output circuit connected to the plate and cathode, said output circuit being tuned to adesired carrier frequency, a reactive network connected between the plate and cathode of the tube and being series resonant to the said carrierfrequency whereby alternating voltage developed. across thereactive network has a relatively low, amplitude at said carrier frequency and increasingly higher amplitudes-atmodulation frequency components of the modulated carrierband spaced from said carrier frequency, and means for impressing said alternating voltage upon said signal grid in degenerative phase, said tube including an auxiliary electrode, means for impressing upon said auxiliary electrode local oscillations whose frequency differs from the input circuitsignal frequency by the value of said output carrier frequency.

7. In combination with a network including a transmission tube having at least a cathode, signal grid and anode, a modulated signal carrier inputcircuit connected between the grid and. cathode, a signal output circuit connected between the anode and cathode, meansfor automatically controlling the selectivity of said network comprising a series resonant circuit-common to the input and output circuits, said common circuit being tuned to the carrier frequency whereby alternating voltage developed thereacross is fed back to said grid in a negative phase and to a greater extent at modulation frequency components of the modulated carrier band than at said carrier frequency, and means responsive to a decrease in carrier amplitude for increasing the degree of negative feedback at said modulation frequencies.

8. In a side band modulated carrier energy transmission system of the type including at least a carrier-tuned amplifier, a demodulator the method which includes impressing modulated carrier voltage upon the amplifier, deriving from the amplified voltage modulated carrier frequency voltage components whose magnitude is directly dependent on the spacing in the modulated carrier band. of a modulation frequency component from the mid-band carrier frequency, cmbining the said components with the impressedmodulatedvoltage in an oping from. the amplified voltage, modulated car- .40 and a modulation frequency ut1l1zat1on circu t,

r-i'er: frequency voltage components. whose mag nitudeis directly; dependent won the; spacing in the modulated carrier band; Ora modulationfrequency component from the mid eband; carrier frequency, combining. the said. components with the impressed modulated1voltageinjan opposing sense, demodulating: the, amplified, voltage, transmitting the demodulated voltage: through said utilization circuit, controlling: the magnitude. of said derived components, controlling the frequency response characteristic, of said utilization circuit, and, maintaining; said two controlling actions sorelated; thatthe; derived components are of maximum, value-an'dthe response of the low modulationfrequenciesL isa minimum in response, tominimum amplitude of. the carrier.

10. Ina side band modulated carrier trans: mission system of V the type comprising ,a modulated, carrier voltage transmission network, a demodulator. and a modulation frequencyvoltage transmission network, meansat, said carrier transmission network; for controlling-the magnitude, of the high modulation frequency components of the carrier side bands, meansat said modulation transmission network for con: currently controlling the magnitude of the, low modulation frequencies, and, means common to said both controlmeans for relating them in a manner such that-the magnitudes under control are decreased in response to, carrier amplitude decrease. a

11., In a system for, the transmission of side band modulated carrier voltage, .and; having a tube providing carrier, voltage input andoutput circuits, the. method whichincludes impressing modulated. carrier voltage upon, the;v input; cir cuit, derivingfrom modulated carrier voltage re: peated by the tube alternating voltage pre dominantly of therhigher modulation frequency components of the carrier side. bands, combin ing the derived voltage ;with the. impressed voltage inasense to reduce the responseat the input circuit; to said higher components, developing at the, output; circuit, carrier voltage with reducedhigher modulation frequency. compo,- nentfmagnitude, and;regulati ng the magnitude of said; derived voltage automatically in response to carrier amplitude variation thereby toadjust the magnitude of said response reduction;

12.- A superheterodyne carrier wave receiver comprising an input circuit, a local oscillator circuit, an electronic tube, for. mixing the incoming oscillations with the V locally generated oscillations, a second electronic tube for amplifying the,

intermediate, frequency produced, a negative feed-,back channel associated with at least one of said electronicv tubes, and a resonant circuit tuned to the, desired frequency to renderthe negative feed-back channel substantially ineffective at said desired frequency.

ALAN W B U VEEIN HORACE ,CON'NELL. 

